Three dimensional displays are receiving increasing interest, and significant research in how to provide three dimensional perception to a viewer is being undertaken. Three dimensional displays add a third dimension to the viewing experience by providing a viewer's two eyes with different views of the scene being watched. This can be achieved by having the user wear glasses to separate two views that are displayed. However, as this is relatively inconvenient to the user, it is in many scenarios desirable to use autostereoscopic displays that directly generate different views and projects them to the eyes of the user. Indeed, for some time, various companies have actively been developing autostereoscopic displays suitable for rendering three-dimensional imagery. Autostereoscopic devices can present viewers with a three dimensional impression without the need for special headgear and/or glasses.
Autostereoscopic displays generally provide different views for different viewing angles. In this manner, a first image can be generated for the left eye and a second image for the right eye of a viewer. By displaying appropriate images, i.e. appropriate from the viewpoint of the left and right eye respectively, it is possible to convey a three dimensional impression to the viewer.
Autostereoscopic displays tend to use means, such as lenticular lenses or parallax barriers/barrier masks, to separate views and to send them in different directions such that they individually reach the user's eyes. For stereo displays, two views are required but most autostereoscopic displays typically utilize more views (e.g. nine views). Indeed, in some displays a gradual transition of view directions is performed over an image such that different parts of an image may be projected in different viewing directions. Thus, in some more recent autostereoscopic displays a more gradual and continuous distribution of image regions over view directions may be applied rather than the autostereoscopic display rendering a fixed number of complete views. Such an autostereoscopic display is often referred to as providing fractional views rather than full views. More information on fractional views may e.g. be found in WO 2006/117707.
In order to fulfill the desire for three dimensional image effects, content is created to include data that describes three dimensional aspects of the captured scene. For example, for computer generated graphics, a three dimensional model can be developed and used to calculate the image from a given viewing position. Such an approach is for example frequently used for computer games that provide a three dimensional effect.
As another example, video content, such as films or television programs, are increasingly generated to include some three dimensional information. Such information can be captured using dedicated three dimensional cameras that capture two simultaneous images from slightly offset camera positions thereby directly generating stereo images, or may e.g. be captured by cameras that are also capable of capturing depth.
Typically, autostereoscopic displays produce “cones” of views where each cone contains multiple views that correspond to different viewing angles of a scene. The viewing angle difference between adjacent (or in some cases further displaced) views are generated to correspond to the viewing angle difference between a user's right and left eye. Accordingly, a viewer whose left and right eye see two appropriate views will perceive a three dimensional effect. An example of such a system wherein nine different views are generated in a viewing cone is illustrated in FIG. 1.
Many autostereoscopic displays are capable of producing a large number of views. For example, autostereoscopic displays which produce nine views are not uncommon. Such displays are e.g. suitable for multi-viewer scenarios where several viewers can watch the display at the same time and all experience the three dimensional effect. Displays with even higher number of views have also been developed, including for example displays that can provide e.g. 28 different views. Such displays may often use relatively narrow view cones resulting in the viewer's eyes receiving light from a plurality of views simultaneously. Also, the left and right eyes will typically be positioned in views that are not adjacent (as in the example of FIG. 1).
Thus, autostereoscopic displays typically do not spread the views over the entire possible viewing or projection angle. In particular, the generated fractional or full views are typically not spread over e.g. a full 180° range, or even over a smaller range of e.g. 90°. Rather, the presented views are typically distributed over a relatively small angle which is known as a viewing cone. The combined viewing angle of the display is then formed by a plurality of repeated viewing cones, each of which provides the same views. Thus, the viewing cones are repeated to provide a projection over the entire viewing angle range of the autostereoscopic display and accordingly the individual views are projected in a plurality of different viewing cones, and in different viewing directions. FIG. 2 illustrates an example of the autostereoscopic display of FIG. 1 projecting a plurality of viewing cones (in the example, three viewing cones are shown).
FIG. 3 illustrates an example of the formation of a pixel (with three color channels) from multiple sub-pixels. In the example, w is the horizontal sub-pixel pitch, h is the vertical sub-pixel pitch, N is the average number of sub-pixels per single-colored patch. The lenticular lens is slanted by s=tan θ, and the pitch measured in horizontal direction is p in units of sub-pixel pitch. Within the pixel, thick lines indicate separation between patches of different colors and thin lines indicate separation between sub-pixels. Another useful quantity is the sub-pixel aspect ratio: a=w/h. Then N=a/s. For the common slant 1/6 lens on RGB-striped pattern, a=1/3 and s=1/6, so N=2.
As for conventional 2D displays, image quality is of the utmost importance for a three dimensional display in most applications, and especially is very important for the consumer market, such as e.g. for three dimensional televisions or monitors. However, the representation of different views provides additional complications and potential image degradations.
Practical autostereoscopic displays may generate a relatively large number of viewing cones corresponding to different viewing angle ranges. A viewer positioned within a viewing cone (as in FIG. 1) will be provided with different views for the right and left eyes and this may provide a three-dimensional effect. Further, as a viewer moves, the eyes may switch between different views within the viewing cones thereby automatically providing a motion parallax and corresponding stereoscopic effect. However, as the plurality of views are typically generated from input data representing the central view(s), the image degradation increases for the outer views for which an increased disparity and thus position shifting from the original image is required. Accordingly, as a user moves towards the extreme views at the edges of a viewing cone, a quality degradation is often perceived. Thus, typically, when a viewer moves sideways relative to the autostereoscopic display, he will have a natural experience with the display providing a 3D experience through both the stereopsis and motion parallax effects. However, the image quality is reduced towards the sides.
A particular problem when displaying three dimensional images is that cross-talk may occur between different views. For autostereoscopic displays, cross-talk is typically a significant issue due to the light from individual (sub-)pixels having a relatively large dissemination area. As adjacent (sub-)pixels typically relate to different views, a relatively high interview cross-talk may often be experienced. Thus, it is inherent for autostereoscopic designs that a certain amount of cross-talk is present between adjacent views as part of the light from adjacent (sub-)pixels radiates through the lens in the same direction.
Thus, due to cross-correlation between different views (with different disparities and thus with some depth objects being at different positions), a blurring effect may in practice occur which results in a loss of the sharpness of the image.
Another issue is that due to the limited viewing angle of a viewing cone, it is possible that a viewer may not be fully positioned within a viewing cone but may for example have one eye in one viewing cone and another eye in a neighbor viewing cone as exemplified in FIG. 4. However, this may result in a stereo inversion wherein the right eye receives an image generated for the left eye and the left eye receives the image generated for the right eye. Thus, as a viewer moves towards the end of a view cone and passes into the neighbor view cone with one eye, a stereo inversion occurs which is perceived as very disturbing and uncomfortable to the user.
In order to address this issue, it has been suggested to modify the view cones to have a larger and smoother transition between neighbor view cones. Such an approach is described in more detail in WO 2005/091050. However, although this approach may mitigate stereo inversion it also has some disadvantages. Most significantly, it reduces the viewing range within each viewing cone in which the full three dimensional effect is perceived, i.e. it reduces the sweet spot.
Hence, an improved approach for generating images for autostereoscopic displays would be advantageous, and, in particular, an approach allowing increased flexibility, improved image quality, reduced complexity, reduced resource demand, improved cross-talk performance, mitigated stereo inversion, increased user friendliness and/or improved performance would be advantageous.